1. Field of the Invention
The present invention relates to a liquid-quantity monitoring apparatus and a liquid-consuming apparatus provided with the same. More particularly, the present invention relates to a liquid-quantity monitoring apparatus employing a piezoelectric device to monitor the quantity of a liquid, and a liquid-consuming apparatus provided with the liquid-quantity monitoring apparatus.
2. Description of the Related Art
An ink-jet recording apparatus as an example of a liquid-consuming apparatus has an ink-jet recording head provided with pressure producing means for producing pressure in pressure chambers, and nozzles for jetting the pressurized ink in ink drops, and a carriage mounted with the ink-jet recording head.
In the ink-jet recording apparatus, the ink contained in an ink tank (ink cartridge) is supplied continuously through an ink supply passage into the ink-jet recording head during a printing operation. The ink tank is, for example, a replaceable ink cartridge that can be easily replaced with a new one by the user when the ink contained therein is exhausted.
A conventional ink consumption managing method of managing the consumption of the ink contained in the ink cartridge accumulates the number of ink drops jetted by the ink-jet recording head and the quantity of the ink sucked during maintenance work by software, and calculates ink consumption. Another conventional ink consumption managing method uses a level measuring electrode placed in an ink cartridge to determine a time point when ink consumption reaches a predetermined quantity.
The conventional ink consumption managing method of managing ink consumption by accumulating the number of ink drops jetted by the ink-jet recording head and the quantity of the ink sucked during maintenance work by the software has the following problem. Ink drops jetted by some ink-jet recording head have different weights, respectively. Although such ink drops respectively having different weights do not affect image quality significantly, the ink cartridge should be filled with a quantity of ink including a margin to compensate for an error in the cumulative ink consumption due to the use of ink drops respectively having different weights. Consequently, some ink remains in some of ink cartridges after the ink cartridge has been judged to be exhausted.
The conventional ink consumption managing method using the level measuring electrode to determine a time point when ink consumption reaches a predetermined quantity is able to measure the quantity of actually consumed ink, and hence is capable of managing the quantity of the remaining ink with high reliability. However, this method is applicable to managing the quantity of limited kinds of inks because the measurement of the level of the ink relies on the electric conductivity of the ink, and requires a complicated sealing structure for sealing the electrode. A noble metal having high electrical conductivity and high corrosion-resistant property and used for forming the electrode increases the manufacturing cost of the ink cartridge. Since this method needs two electrodes, the ink cartridge needs increased manufacturing steps and an increased manufacturing cost.
A piezoelectric device is proposed to solve the foregoing problems. This piezoelectric device is incorporated into a liquid container. A measuring means capable of accurately measuring the level of ink is proposed. The measuring means includes a means for estimating ink consumption on the basis of the number of jetted ink drops and a piezoelectric device for measuring actual ink consumption.
Those techniques measure the quantity of ink on the basis of a residual vibration signal generated by the residual vibrations of a vibrating part of the piezoelectric device. However, the amplitude of the residual vibration signal is small and hence the measurement is affected significantly by noise and hence it is possible that the quantity of ink cannot be accurately measured.
The present invention has been made in view of the foregoing circumstances and it is therefore an object of the present invention to provide a liquid-quantity monitoring apparatus capable of monitoring the quantity of a liquid contained in a liquid container with high reliability, and a liquid consuming apparatus provided with the liquid quantity monitoring system.
According to a first aspect of the present invention, a liquid-quantity monitoring apparatus comprises: a piezoelectric device having a vibrating part capable of being exposed at least partly to a liquid-containing space for containing a liquid, the piezoelectric device being capable of vibrating the vibrating part by a given drive signal and of generating a signal representing back electromotive force generated by vibration of the vibrating part; and liquid-quantity determining means for determining a quantity of the liquid remaining in the liquid-containing space, to which the vibrating part is exposed, based on a resonance frequency of a residual vibration signal which is output from the piezoelectric device due to a residual vibration of the vibrating part after the vibrating part has been vibrated by the drive signal. The liquid-quantity determining means counts a number of pulses included in the residual vibration signal, measures a time period necessary for counting a predetermined number of pulses after starting counting the pulses, and determines the quantity of the liquid based on the time period which has been measured. The liquid-quantity determining means repeats a pulse-counting operation for counting the predetermined number of pulses with different starting time points, and decides that a measurement is incorrect when differences between the time periods measured by the pulse-counting operations are greater than a predetermined allowable limit.
Preferably, the pulse-counting operation is repeated at least three times. The starting time points when the pulse-counting operation is to be started for first, second and third pulse-counting cycles are so determined that a time period necessary for counting the predetermined number of pulses in the first pulse-counting cycle and a time period necessary for counting the predetermined number of pulses in the third pulse-counting cycle do not overlap each other, and a time period necessary for counting the predetermined number of pulses in the second pulse-counting cycle overlaps the time periods necessary for counting the predetermined number of pulses in the first and the third pulse-counting cycles.
Preferably, the liquid-quantity determining means measures again the time periods each necessary for counting the predetermined number of pulses when the measurement is judged to be incorrect.
Preferably, the liquid is contained in an ink container for an ink-jet recording head, the piezoelectric device being combined with the ink container such that at least part of the vibrating part of the piezoelectric device is exposed to an ink chamber formed in the ink container. The liquid-quantity determining means measures again the time periods each necessary for counting the predetermined number of pulses while a carriage holding the ink-jet recording head is stopped, when the measurement is judged to be incorrect.
Preferably, the liquid-quantity determining means measures again the time periods each necessary for counting the predetermined number of pulses while an ink jetting operation of the ink-jet recording head is stopped, when the measurement is judged to be incorrect.
Preferably, the liquid is contained in an ink container for an ink-jet recording head, the piezoelectric device being combined with the ink container with at least a part of the vibrating unit thereof exposed to an ink chamber formed in the ink container. The liquid-quantity determining means measures again the time periods each necessary for counting the predetermined number of pulses while an ink jetting operation of the ink-jet recording head is stopped, when the measurement is judged to be incorrect.
Preferably, the liquid-quantity determining means is capable of deciding whether or not a level of the liquid passed a position where the vibrating part is positioned, based on a change of a resonance frequency of the residual vibration signal that occurs when the level of the liquid passes the vibrating unit.
According to the second aspect of the present invention, a liquid consuming apparatus comprises: the liquid-quantity monitoring apparatus mentioned above; a liquid container combined with the piezoelectric device of the liquid-quantity monitoring apparatus; and a liquid consuming unit that consumes a liquid supplied from the liquid container.
According to the third aspect of the present invention, a computer readable recording medium storing a program to be executed by a computer system including at least one computer to realize functions of the liquid-quantity determining means of the liquid-quantity monitoring apparatus mentioned above.